Technical Field
The present disclosure relates to light emitting devices (LEDs), and more particularly to improving light extraction from LEDs.
Description of the Related Art
Light rays generated in a luminescent medium with higher index of refraction than the exit medium, typically air, are submitted to the total internal reflection phenomenon (TIR). Consequently, rays which are in the conditions of TIR will be trapped and guided into the material. Because light is generated without any preferential direction, this trapping effect affects the out coupling efficiency of the light emitting device, such as LED and OLED devices, for instance, and all sources which could be seen as an internal source with higher refractive index than the exit medium. The trapped light is then re-adsorbed in the device and could turn into heat that may impact the device performances and lifetimes.